Monday, March 03, 2014

The Obesity Rate for Children Has Not Plummeted  -- Despite what the New York Times tells you

I saw the research report concerned a couple of days ago and found it so straightforward that I was going to reproduce the abstract here without comment.  So I was quite amazed that the NYT claimed that the research said the opposite of what it actually said.  Even supermarket tabloids tend to be better than that.   I was pleased therefore to see that Razib Khan has torn into the NYT over their sensationalism.  Razib's comments below are followed by the journal abstract  -- JR

Common sense tells you that if you run enough trials, by chance, you will occasionally get an unexpected outcome. When scientists deem a result “statistically significant,” they're just saying that given their default expectations (e.g. around 50/50 for a coin toss), the outcomes obtained are unlikely to have occurred by random chance. A fair coin is unlikely to land on heads nine out of 10 tosses, so such an outcome suggests the coin is probably not fair. Unlikely is not the same as impossible, and if you look long and hard you will inevitably stumble upon random events that seem novel but are just the outcome of chance.

I bring this up because earlier this week the New York Times trumpeted: “Obesity Rate for Young Children Plummets 43% in a Decade.” A surprising discovery, and a pretty big deal, right? The article spread like wildfire on Twitter and Facebook. For once, some heartening news about the health of this nation! My immediate reaction, however, was that there must be something we don’t know about obesity to get such a massive change in such a short period of time. Then I started reading.

From the perspective of the researchers themselves, the continuing obesity problem seems to be the most important finding.
The warning signs are right there in the Times piece, where by the third paragraph the reporter, Sabrina Tavernise, reveals that “About 8 percent of 2- to 5-year-olds were obese in 2012, down from 14 percent in 2004.” The six-percentage-point difference in absolute terms results in the 43 percent relative difference. The Times’ headline blared the relative figure because the absolute drop is just not that impressive.

My curiosity was piqued enough to look at the original report from which the Times (and the Washington Post, USA Today, and CNN, to name a few) drew the findings. It appears in the Journal of the American Medical Association and comes from a group of researchers with Centers for Disease Control and Prevention affiliations—both legitimate institutions. The report's closing two sentences are telling: “Overall, there have been no significant changes in obesity prevalence in youth or adults between 2003-2004 and 2011-2012. Obesity prevalence remains high and thus it is important to continue surveillance.” Would you have anticipated such a downbeat conclusion from the newspaper headlines? I doubt it. When evaluating the total sample across age groups, rather than just 2- to 5-year-olds, there hasn’t been any change at all. From the perspective of the researchers themselves, the continuing obesity problem seems to be the most important finding.

The study itself illuminates why we should be skeptical of the headlines about the study. Here is how its authors lay out exactly why one should be cautious about even the most optimistic findings, the 43 percent drop in obesity in the 2-to-5 age bracket:

In the current analysis, trend tests were conducted on different age groups. When multiple statistical tests are undertaken, by chance some tests will be statistically significant (eg, 5% of the time using ╬▒ of .05). In some cases, adjustments are made to account for these multiple comparisons, and a P value lower than .05 is used to determine statistical significance. In the current analysis, adjustments were not made for multiple comparisons, but the P value is presented.

More plainly, the researchers are acknowledging that, yes, if you do enough comparisons and interpretations across various age cohorts, you're bound to turn up an exciting statistically significant result eventually. If you do 10 flips of enough coins, you will at some point flip one to land on heads 10 times. This isn’t fate—it’s probability, and it’s inevitable in the long run. In order to separate out the noise from the real significant results, the authors should have held themselves to a higher standard. Instead they repeatedly declare that they did not and admit that the significant decline in obesity in the age group in question should be treated with caution. In isolation, the result in the decline in obesity has a 1 in 33 chance of being due to random chance (P value: 0.03). But remember that they kept checking for changes in obesity over the years, so looking at the whole study, the random chance of getting these results is much higher than 1 out of 33.

So, two primary takeaways. The first concerns how the sausage is made in modern science, and the question is: Why was this even published in the first place, with all the caveats? Because a great deal of research manages to get published. Where there’s a will, there’s a way. So when you read a headline that appears too good to be true, remember: Just because it appears in a reputable journal does not mean that a study has “proved” anything.

A far bigger issue is that studies like these, and the headlines that result, drive the discussion about public health and policy in this country. The media seizes on sexy results, amplifies them without due skepticism, and the public is misled. This can impact billions of dollars allocated to campaigns meant to capitalize on the supposed implications of scientific studies. It's hardly an academic footnote in this case. Commentators are already attempting to adduce the reasons for the decline in obesity in this age, pointing to the dietary changes in preschool menus, awareness campaigns, and exercise programs that specifically target tots.

Let’s not congratulate these policies just yet, because the most likely upshot is that this finding won't be verified over time. In other words, it is probably a statistical fluke. I will be thrilled if studies with more methodological rigor prove me wrong.


Prevalence of Childhood and Adult Obesity in the United States, 2011-2012

Cynthia L. Ogden et al


Importance: More than one-third of adults and 17% of youth in the United States are obese, although the prevalence remained stable between 2003-2004 and 2009-2010.

Objective: To provide the most recent national estimates of childhood obesity, analyze trends in childhood obesity between 2003 and 2012, and provide detailed obesity trend analyses among adults.

Design, Setting, and Participants: Weight and height or recumbent length were measured in 9120 participants in the 2011-2012 nationally representative National Health and Nutrition Examination Survey.

Main Outcomes and Measures: In infants and toddlers from birth to 2 years, high weight for recumbent length was defined as weight for length at or above the 95th percentile of the sex-specific Centers for Disease Control and Prevention (CDC) growth charts. In children and adolescents aged 2 to 19 years, obesity was defined as a body mass index (BMI) at or above the 95th percentile of the sex-specific CDC BMI-for-age growth charts. In adults, obesity was defined as a BMI?greater than or equal to?30. Analyses of trends in high weight for recumbent length or obesity prevalence were conducted overall and separately by age across 5 periods (2003-2004, 2005-2006, 2007-2008, 2009-2010, and 2011-2012).

Results:  In 2011-2012, 8.1% (95% CI, 5.8%-11.1%) of infants and toddlers had high weight for recumbent length, and 16.9% (95% CI, 14.9%-19.2%) of 2- to 19-year-olds and 34.9% (95% CI, 32.0%-37.9%) of adults (age-adjusted) aged 20 years or older were obese. Overall, there was no significant change from 2003-2004 through 2011-2012 in high weight for recumbent length among infants and toddlers, obesity in 2- to 19-year-olds, or obesity in adults. Tests for an interaction between survey period and age found an interaction in children (P = .03) and women (P = .02). There was a significant decrease in obesity among 2- to 5-year-old children (from 13.9% to 8.4%; P = .03) and a significant increase in obesity among women aged 60 years and older (from 31.5% to 38.1%; P = .006).

Conclusions and Relevance: Overall, there have been no significant changes in obesity prevalence in youth or adults between 2003-2004 and 2011-2012. Obesity prevalence remains high and thus it is important to continue surveillance.


Hope for pancreatic cancer patients as jab that kills rogue cancer cells is developed

All theory so far

A vaccine that fights pancreatic cancer has begun clinical trials in the UK.  Experts at The Clatterbridge Cancer Centre - who treat over 28,000 patients a year - are working with other UK researchers to create the vaccine. It will be used in conjunction with traditional treatments.

The pancreas is a gland which produces and releases vital substances such as digestive enzymes and insulin - which regulates blood sugar levels.

Symptoms tend to manifest once the cancer is advanced and include unexpected weight loss, upper abdominal pain and jaudice - all of which could be a multitude of illnesses. So the condition is often diagnosed late.

Treatment ideally involves removal of the tumour, though such surgery is only suitable for up to 20 per cent of patients. Chemotherapy and radiotherapy may also be offered.

The idea behind the vaccine is that it will be offered after surgery. 

One reason for the very low survival rate is that although the cancer may appear to have gone into remission, the cells may have spread across the body and later form secondary tumours.

The immune system doesn't recognise the cells so they are able to multiply.

`The vaccine will work to manipulate the body's immune system to recognise microscopic cancer cells, meaning a patient is able to fight any remaining cells before the cancer forms again in any other parts of the body,' says Professor Daniel Palmer, chair of medical oncology and one of the trial leads.

It works along the same lines as any vaccine - by injecting a little of the disease into the body the immune system is stimulated.

Usually patients would be offered chemotherapy, and should this be thought appropriate, they will still receive it alongside the vaccine, which has minimal side effects - fatigue and nausea may be experienced.

Immunotherapy is being explored for many types of cancer. Previous research has shown that it can destroy surviving cancer cells and has minimal side effects.

The first `cancer vaccine' was approved in 2010 for prostate cancer and immunotherapy is currently showing great promise in lung cancer treatment.

`Immunotherapy is an exciting area of research in the field of pancreatic cancer. We look forward to hearing about the results,' says Maggie Blanks, CEO of the Pancreatic Cancer Research Fund.


No comments: